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Earth of fire

Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #volcanic activity
GeoEye-1 satellite image of the Davidof volcano. Thick pumice and pyroclastic deposits are visible as light colored areas exposed by Gray Point on the east side of Davidof Island. Crater Bay is a submerged caldera 2.5 km in diameter. - 22,08,2020 / Matt Loewen / AVO - one click to enlarge

GeoEye-1 satellite image of the Davidof volcano. Thick pumice and pyroclastic deposits are visible as light colored areas exposed by Gray Point on the east side of Davidof Island. Crater Bay is a submerged caldera 2.5 km in diameter. - 22,08,2020 / Matt Loewen / AVO - one click to enlarge

Davidof volcano - hypocenters of the earthquakes of the last 3 days to 10.12.2021 / 12h - Doc. AVO - one click to enlarge

Davidof volcano - hypocenters of the earthquakes of the last 3 days to 10.12.2021 / 12h - Doc. AVO - one click to enlarge

A swarm of earthquakes has occurred near the Davidof volcano during the latter part of the week and is continuing. The largest earthquake to date occurred this morning (December 10) at around 7:45 p.m. UTC (10:45 a.m. AKST) and had a magnitude of 4.2. This swarm may be associated with volcanic unrest or it could also be due to regional tectonic activity.

Due to the possibility of an escalation of volcanic unrest, AVO has increased the alert level to Advisory, and the aviation color code to Yellow.

AVO continues to monitor the situation with seismometers deployed on neighboring islands as there is no real-time seismic monitoring network on the Davidof volcano. The nearest seismometers to Davidof are located about 13 km (8 miles) east of the volcano on Little Sitkin Island.

 

Davidof Volcano is a mainly submerged stratovolcano in the Rat Island Group in the western Aleutian Islands, about 350 km west of Adak. The subaerial part of the volcano includes the Davidof, Khvostof, Pyramid and Lopy Islands, which surround Crater Bay, a caldera 2.5 km in diameter. The islands are made up of intercalated lava flows and explosive deposits. The volcano has been little studied, but visits by geologists to the Alaska Volcano Observatory in 2021 documented thick sequences of dacite rhyolite, pyroclastic flows, and fall deposits that represent the most recent explosive eruptions. The age of these deposits is unknown, but they appear to be older than the nearby Holocene Segula and Little Sitkin deposits. There are no known historical eruptions from the Davidof.

 

Source: AVO

Davidof - seismogram of 10 and 11.12.2021 / LSSA seismic station located on Little Sitkin Island, more than 12 km east of Davidof. - AVO

Davidof - seismogram of 10 and 11.12.2021 / LSSA seismic station located on Little Sitkin Island, more than 12 km east of Davidof. - AVO

The eruption of the Semisopochnoi volcano continues. Small explosions producing low-level ash clouds from the north crater of Mount Cerberus on Semisopochnoi Island have occurred several times a day throughout the past week. These explosions were detected by local seismic sensors, local and regional infrasound sensors and, when weather conditions permitted, by webcam and satellite images. Clouds obscured the volcano for most of the past week, although small ash clouds drifting at least 185 km southeast of Semisopochnoi were detected in satellite data on the 8th and 9th. December.

Small explosions that result in minor ash deposits near the active northern crater of Mount Cerberus, and ash clouds generally below 10,000 feet above sea level have characterized recent activity and do not show no sign of slowing down.

Semisopochnoi is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

The alert level is: Watch, and the aviation color code: Orange.

 

Source: AVO

In addition to these two volcanoes, the Great Sitkin and the Pavlof are still in the Orange aviation code and the Watch alert level, under the special surveillance of the AVO.

Semisopochnoi - explosion accompanied by an ash plume on 11.10.2021 / 09:25 HST - SEPE / Avo webcam by Matt loewen

Semisopochnoi - explosion accompanied by an ash plume on 11.10.2021 / 09:25 HST - SEPE / Avo webcam by Matt loewen

The OVSAN reports a white degassing at the level of the crater of Santiaguito, which disperses in a west and south-west direction, weak and moderate explosions were recorded which expel white and gray columns at a height of 3,400 meters above. above sea level which are scattered to the southwest and west.

The VAAC Washington reports this December 11 a discreet emission of ash at a flight altitude of 150 / 4,600 m.

Boulder and ash avalanches continue to be generated on the flanks: West, South-West and South mainly and others weak and moderate in the North-East and South-East directions, some reaching the base of Dome Caliente, some explosions and avalanches leave fine ash in suspension in the volcanic perimeter.

A slight degassing noise similar to that of an airplane turbine can be heard due to the pressure of the magmatic gases.

Due to the block lava extrusion at the Caliente Dome in a west-southwest direction and unstable material in the crater, there is a likelihood of moderate to strong pyroclastic flows, so you should not stay close or inside the channels. rivers near the slopes of the volcano.

 

Sources: Insivimeh & VAAC Washington

Santiaguito - Caliente dome glow and westward lava extrusion of the dome - Landsat-8 SWIR image 09.12.2021 / USGS / Insivumeh -one click to enlarge

Santiaguito - Caliente dome glow and westward lava extrusion of the dome - Landsat-8 SWIR image 09.12.2021 / USGS / Insivumeh -one click to enlarge

On December 10, the IGN located a total of 15 earthquakes on the island of La Palma, none of them felt by the population. The maximum recorded magnitude is 3.4 (mbLg), corresponding to today's earthquake at 07:04 UTC, at a depth of 39 km.
The seismicity continues under the central area of ​​Cumbre Vieja in the same areas of the previous days, most of the earthquakes (13) are located at depths between 9 and 15 km, the rest (3) were located at depths included between 29 and 39 km. No earthquake was located at depths less than 9 km.
The amplitude of the tremor signal remains at low levels, with a slight increase in the last few hours.

On December 11, seismicity remained low at intermediate depths and more than 20 km. and the tremor level is at low values ​​and stinks of variability. (Pevolca)

As in previous days, the island's network of permanent GNSS stations does not show a clear trend in the deformation of the stations closest to the eruptive centers.

In view of the image calibrated at 08:45 UTC, an ash cloud height of 1200 m is estimated. with a south-southwest direction.
The height of the cone is measured by obtaining a value of 1,123 m. On sea level.

Diffuse CO2 flux measurements were carried out on the eastern slope of the main building in order to determine the most appropriate point from which to take a fumarole gas sample.

During the last hours, the area affected by the lava has not increased, and remains at 1,184 ha.

 

Sources: IGN, IGME, DSN, Pevolca

La Palma - seismicity at 12.10.2021 / 08.38am - Doc. IGN

La Palma - seismicity at 12.10.2021 / 08.38am - Doc. IGN

La Palma - RSAM at 12.10.2021 / 8:35 am - Doc. IGN

La Palma - RSAM at 12.10.2021 / 8:35 am - Doc. IGN

La Palma - Cumbre Vieja flows - SAR image 01.12 / 09.12.2021 MTC False color composite Cosmo-SkyMEd via DSN - one click to enlarge

La Palma - Cumbre Vieja flows - SAR image 01.12 / 09.12.2021 MTC False color composite Cosmo-SkyMEd via DSN - one click to enlarge

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